If they are only 1/4 inch off then it is probably not you or your 1/4 inch. It is probably because she is giving you the exact measurements of a mathematically correct block and you need to use what is called a "scant" 1/4 inch.
The exact figures do not take into account that ironing the seams takes up space, so your sewing line needs to be just a little bit less than 1/4 inch (hence the name "scant 1/4 inch"). If your machine lets you move the needle over, move it one or two positions to have that slightly smaller space. Don't forget to set it everytime you make one of her blocks!
If your machine doesn't do that, you can eyeball the smaller seam by going over to the right just a tiny bit (say, two threads or so). You can still use all the blocks you've made using the methods other people have mentioned. Hope this helps.